Facebook CEO Mark Zuckerberg has been criticized for his leadership, especially in the wake of the seemingly off-the-cuff Instagram buy. But employees love him and how he runs the social networking company.

According to Glassdoor, Zuckerberg tops its list of "50 Highest Rated CEOs," as rated by employees. Zuckerberg has a 99 percent approval. SAP Co-CEOs
Bill McDermott and Jim Hagemann Snabe also have a 99 percent approval.

"While anyone can assume a position in leadership, not everyone garners their employees' support for how they the company," said Robert Hohman, Glassdoor CEO and co-founder. "The CEOs who are most successful in gaining employee approval are those who paint a clear vision of what the company is setting out to achieve and how it's going to get there.

"To be recognized by your employees as a strong leader also comes as a result of having a solid company culture that helps employees foster the skills necessary to move business forward and meet the needs of customers."

During the past year, Mark Zuckerberg saw his CEO approval rating climb 14 percentage points, to a 99 percent approval. One employee in Facebook's Menlo Park, Calif., headquarters said: "An open community from Zuck on down. Mutual trust companywide and sense of community and drive, instilled by our CEO, who we all truly respect."

As part of Glassdoor's company review survey, employees indicate whether they approve or disapprove of the way their CEO is leading the company. We asked Dora Vell, CEO of Vell Executive Search, why she thought Zuckerberg hit the top spot in the employee survey. Beyond his likeability, she gave us two phrases that could shed some light on his rating: current results and future results.

"Zuckerberg has achieved short-term results while positioning the company for the future," Vell said. "He's developed and implemented strategy, avoided pitfalls and navigated challenging issues."

Seventeen CEOs on Glassdoor's 2012 report also made this year's report, including Cook, who took top honors last year, but fell to the 18th spot this year as he saw his approval rating decrease four percentage points to a 93 percent approval.